Stickers that show what you have to lend

"... Switzerland's Pumpipumpe is trying to bring a little of that back -- forward? -- into the information age. Rather than developing a mobile app that assists sharing of goods between neighbors, they've gone old-school with stickers that people can apply to their mailboxes to let others know what they have to lend. It's a simple ploy to encourage more social interaction and sharing between neighbors who are interested in lending and borrowing things within their local community."